code: def loss(self, pred, label):
      return F.nll_loss(pred, label)
  
imports: import torch
  import argparse
  import skip_models
  import torch.nn
  import torch.nn.functional
  import torch_geometric.transforms
  import torch_geometric.nn
  import torch.optim
  from torch.utils.data import DataLoader
  from torch_geometric.datasets import TUDataset
  from sklearn.metrics import *
  from torch.nn import Sequential, Linear, ReLU
  from deepsnap.dataset import GraphDataset
  from deepsnap.batch import Batch
label_desc: Use image node_id 4 for calling the GNN obj's underlying member method code with example usage: obj.loss(pred, label) and returns: F